<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .green {
            background-color: green;
        }
    </style>
</head>

<body>
    <div class="the_div">
        <p>我是p标签</p>
        <h3>我是h3</h3>
        <h3>我是h3</h3>
        <h3>我是h3</h3>
        <a id="theA" href="#">我是一个a标签</a>
        <ul>
            <li>北京</li>
            <li>天津</li>
            <li>南京</li>
        </ul>
        <ol class="my_li">
            <li>大张</li>
            <li>大王</li>
            <li>大狗</li>
        </ol>
        <ul class="my_li">
            <li>小明</li>
            <li>小红</li>
            <li>小蓝</li>
        </ul>
    </div>
    <script>
        const a = document.querySelector('.the_div a');
        const h3s = document.querySelectorAll('h3');
        console.log(h3s);
        const lis = document.querySelectorAll('li');
        const lix = document.querySelectorAll(' ul .my_li li');
        const lih = document.querySelector('.my_li li:nth-child(2)');
        lih.innerHTML = `小六`
        lih.style.color = 'red'
        const tianjin = document.querySelector('ul li:nth-child(2)');
        console.log(tianjin);
        tianjin.classList.add('green')
    </script>
</body>

</html>